If you want to switch your e-mail account to Gmail, Google has made it easier than ever. E-mail accounts aren't easy to get rid of — they store information you might need in the future, and the fact that most of them are free means it's easier to keep them and go on using them — for example, as a send-your-spam-here account.
However, if you're ready to make the switch to Gmail from, say, AOL or another service, Google provides a tool to help you move everything over to a new Gmail account. By following the steps on the information page on importing contacts and mail, you'll be able to take advantage of all the features and convenience of a Gmail account with everything you have at the old account.
Even if you don't want to give it up now, you can point your account to Gmail and run everything from there.